1. Field of the Invention
The invention relates to a thermal type gas flow measuring instrument or measuring gas flow, such as air flow.
2. Description of Related Art
As an example of the gas flow type measuring instrument, a thermal type air flow measuring instrument is known for measuring the intake air flow in automobile internal combustion engines.
This thermal type air flow measuring instrument takes advantage of the fact that the amount of heat dissipated from a heating resistor increases at a steady rate relative to the intake air flow. Because of its capability to directly measure the mass flow, it is widely utilized as a flow measuring device for automobile fuel control purposes.
As a technology for improving the accuracy of flow measurement in the above-mentioned thermal type air flow measuring instrument, Patent Document 1 discloses an invention entitled “Method for controlling an internal combustion engine using air flow measuring apparatus.”
The technology described in Patent Document 1 involves a self-diagnosis of the air flow measuring apparatus for measuring intake air flow in an internal combustion engine, on the basis of an output signal that is obtained in the absence of intake air flow. Based on the results of the self-diagnosis, the intake air flow signal is modified, or a warning is provided to indicate abnormality.
In the technology of Patent Document 1, the thermal type air flow measuring instrument and an engine control unit must be continuously supplied with electric power until a certain time has elapsed following the termination of the engine. This is because the intake air flow must be zero when a self-diagnosis is performed.
Patent Document 1: JP Patent Publication (Kokai) No. 11-295125 A (1999)